1. Field of the Invention
This invention relates to multicolor display devices utilizing light emitting diodes.
2. Description of the Prior Art
An electronic display having segments wherein each segment is capable of selectively illuminating two colors is disclosed in U.S. Pat. No. 4,488,149 issued on Dec. 11, 1984 to William A. Givens, Jr. Two AND gates are provided for biasing, in each display segment, either a first light emitting diode, for emitting a first color, or a second light emitting diode, for emitting a second color. It is not contemplated to illuminate both light emitting diodes in each segment simultaneously for blending the colors. A multi-element display is not contemplated.
A driving circuit for light emitting diodes, disclosed in U.S. Pat. No. 3,740,570, issued on Jun. 19, 1973 to George R. Kaelin et al., uses special light emitting diodes which emit different color light in response to different currents. The driving circuit selects either a relatively high current for green display, or a relatively low current for red display, or an intermediate current for yellow display, by selectively applying pulses of different amplitudes to the light emitting diodes. The display device is not capable of producing other colors. It is not contemplated that light signals of primary colors may be blended.
A multi-color LED display for seven segment figures is disclosed in German Patent No. 3,009,416 issued on Sep. 17, 1981 to Klaus Gillessen. The LED circuit consists of seven group of diodes, each group made up of two diodes, one red and one green. The cathodes of all red diodes are terminated in a common connection, and the green ones likewise, the anodes of each pair of diodes being common for that pair. Two transistors connected in cascade are utilized for activating either all green LEDs, or all red LEDs, but not both simultaneously. When a low level signal is applied to the base of the first transistor, the first transistor is blocked, and the second transistor is turned ON to illuminate the second set of the diodes. When a high level signal is applied to the input of the first transistor, the first transistor is turned ON, while the second transistor is blocked, whereby the first set of the diodes is illuminated. Since the first transistor cannot be simultaneously turned ON and OFF, it would be impossible to illuminate the two sets of the diodes simultaneously. In another embodiment is shown a multi-color LED display utilizing three sets of LEDs: red, green, and blue, which are respectively commonly connected and may be activated by manual switches. It is not contemplated that the three sets of LEDs be activated in selective combinations to blend the colors.
A digital electrooptical display with anti-parallel light emitting diodes is disclosed in East German Patent No. 220,844 issued on Apr. 10, 1985 to Thomas Hoffmann et al. Two light emitting diodes for emitting light of different colors are connected in each segment back-to-back. Since the light emitting diodes are connected to conduct currents in opposite directions, it would be impossible to illuminate them simultaneously, because the opposite currents attempting to pass through a single conductor would cancel.
The prior art does not contemplate a multicolor display element which includes a plurality of display areas with light emitting diodes of respective primary colors, and which also includes a single enable input, for receiving an enable signal, for either extinguishing the entire display element or for illuminating the selected display areas in a desired color.
It is the principal object of this invention to provide an improved multicolor display device.
It is another object of the invention to provide a multicolor display element using two primary color light emitting diodes and including an enable input.
It is still another object of the invention to provide a multicolor display element using three primary color light emitting diodes and including an enable input.
It is still another object of the invention to provide a multicolor display element including a plurality of buses, to which the light emitting diodes of primary colors are connected in accordance with their colors, and a plurality of color control inputs for the respective buses.
It is still another object of the invention to provide a multicolor display element including a plurality of tri-state buffers, each interposed between the color control input and the bus.
It is still another object of the invention to provide a multicolor display element including a plurality of tri-state buffers, each of them may be selectively controlled to be conductive and non-conductive.
Other objects of the invention will be obvious from the appended drawings and their description.
In summary, a multicolor display element of the invention includes a plurality of display areas, each including light emitting diodes of respective primary colors. The buses are provided, to which the light emitting diodes are coupled in-accordance with their colors. Each bus includes a color control input for receiving color control signals.
The invention resides in the addition of tri-state buffers, each interposed between the color control input and the corresponding bus, which may be commonly controlled, by a single enable input, to be conductive and non-conductive.
A new and unexpected result was achieved by the instant invention: it is possible to interconnect the color control inputs of multiple display elements, to commonly present the color control signals to the interconnected color control inputs, and to control the individual display elements by their respective enable inputs to be either extinguished or illuminated in a color in accordance with the color control signals. The prior art does not contemplate such a display system.